1. Field of the Invention
The present invention relates generally to the field of optical attenuation devices for use in optical systems. In particular, the present invention relates to a control system for an electrochromic device.
2. Background Technology
Fiber optics are increasingly used for transmitting voice and data signals. As a transmission medium, light provides a number of advantages over traditional electrical communication techniques. For example, light signals allow for extremely high transmission rates and very high bandwidth capabilities. Also, light signals are resistant to electromagnetic interference that would otherwise interfere with electrical signals. Light also provides a more secure signal because it does not emanate the type of high frequency components often experienced with conductor-based electrical signals. Light also can be conducted over greater distances without the signal loss typically associated with electrical signals on a copper conductor.
Many conventional electrical networks are being upgraded to optical networks to take advantage of increased speed and efficiency. Optical communication networks use lasers to create light which is then modulated to convey information. One of the many components of an optical communications network is an optical attenuator. Optical attenuators control the intensity of one or more wavelengths of light within an optical system. One use for optical attenuators is in combination with an optical receiver having a photodetector and a preamplifier. The optical attenuator can be used to attenuate the incoming optical signal if the intensity of the signal exceeds a specified threshold. In this manner, the intensity of the incoming signal is brought in line with the dynamic range of the components of the optical receiver, and avoids the need of using more expensive receivers that would have larger dynamic operating ranges.
In addition to the foregoing use of optical attenuators, it is sometimes necessary to recalibrate or replace one or more of the lasers generating light in the system. To avoid data corruption, it is necessary to completely extinguish the laser's light from the optical system before recalibration or replacement. Optical attenuators are capable of extinguishing the laser's light by blocking it from entering the remainder of the optical system. There are numerous general methods of attenuating or completely extinguishing light, including polarization, reflection, diffusion, etc. In addition, it is often necessary to control the intensity of a particular wavelength or channel of light entering a fiber. Although it is possible to simply adjust the electrical current feeding a laser to adjust the output intensity, this is not desirable because this method of attenuation will affect the bandwidth capabilities of the laser. Therefore, it is necessary to use a variable optical attenuator to attenuate or adjust the output intensity of a particular laser.
One type of attenuator uses an electrochromic (EC) window to attenuate light that is transmitted through the window. An EC window attenuates the amount of light that is allowed to transmit through the window as a function of the input voltage that is applied to the window. This type of attenuator does not use moving parts nor does it change the polarization in any way to attenuate the incoming light. An EC window utilizes a particular crystalline structure that reflects and refracts light in such a way as to attenuate the light when a voltage is applied across the window. Many applications for EC windows require them to maintain a particular attenuation level for a long period of time. One of the difficulties associated with controlling the attenuation provided by an electrochromic attenuation device is that the attenuation is exponentially related to the voltage applied to the attenuation device. Accordingly, achieving an accurate and prolonged level of attenuation has been difficult using conventional approaches. Moreover, conventional attenuation techniques involve applying a particular voltage to the EC window for the entire duration of active operation of the EC window in order to maintain the proper attenuation level.
Therefore, there is a need in the industry for an EC control circuit that minimizes the amount of power that must be expended in order to maintain a particular attenuation level. In addition, the control circuit should be relatively easy to manufacture and implementable in a wide variety of applications.